It is known from prior art that certain manufacturing operations require samples of product to be retracted from product chambers for monitoring the manufacturing process and in particular for checking the resulting product from time to time.
DE 43 16 734 A1 for example discloses an apparatus of this type for extracting a sample of product, said apparatus comprising a sample chamber arranged in a housing for movement between a position projected into the product chamber and a position retracted from the product chamber, which housing is connected to a lateral side of the product chamber in such a manner that it surrounds an opening thereof in a sealing relation, and comprising a product outlet in said housing. This type of apparatus is concerned with a sampling valve for extracting liquid or relatively fluent substances from vessels or pipelines. This pre-known sampling valve is comprised of a valve body having an inlet and an outlet which are separated from each other by means of a plunger arrangement. Charging of the medium is effected by extending one of said plungers, the other one of said plungers being moved along by said first plunger during the extension thereof to a position in which the outlet is closed. Accordingly, this sampling valve has an axially movable displacement plunger that extends from the inlet to the outlet. This displacement plunger is followed by a shut-off plunger, and by the relative movement of these plungers a receiving chamber can be formed there between, and in the course of this relative movement said shut-off plunger can be transferred by means of a catch device on the displacement plunger to a position in which the outlet is closed. Accordingly, it is the relative movement between these two plungers which is important. However, for diverse samples of product this technique is not desired. In addition, it can be seen that the correct operation of this pre-known sampling valve is governed by its fitting position, because the sample of product to be extracted is required to flow automatically into the receiving chamber formed between the displacement plunger and the shut-off plunger. Particularly in the case of viscous media it may happen that amounts are extracted which do not correspond to exactly measured amounts as the same are required for sample analysis.
WO 84/04591, too discloses an apparatus for extracting a sample of product from a product chamber. However, in this pre-known device the sample chamber is configured as a continuous bore which is not suited for extracting all kinds of samples of product. Moreover, in this apparatus, too the sample chamber must be fitted in a particular position in order that a measured amount of sample of product can be extracted. Hence, this type of apparatus serves for measuring permeability.
Further, from EP 0 724 145 A2 are known a method or apparatus for filtrate measuring. To this end the apparatus comprises two plungers and a plunger rod, both plungers being movable relative to each other. The chamber which is arranged between these two plungers and which is variable is projected into a tube in which a substance to be measured flows. By retracting both plungers, which are moved relatively to each other, from the tube the sample of product is extracted, so that a filtrate is supplied to a filtrate storage tank in which the required measurements are made. Thereafter, the filtrate is returned to the pipeline. A similar apparatus is also known from EP 0 754 941 A1.
Another sampling valve is described in U.S. Pat. No. 5,585,576. In this sampling valve the sample chamber is arranged between a seal and a cutter means. Said seal and said cutter means are mounted and spaced from each other on a movable axis.
Finally, DE 297 23 631 U1 discloses another well tried apparatus for extracting a sample of product from a product chamber, wherein said sample of product is extracted by means of a sample chamber arranged in a housing and movable within said housing between positions projected into and retracted from the product chamber. In this apparatus the housing rests against a lateral side of the product chamber, surrounding an opening thereof in a sealing relation. The housing also has a product outlet. The sample chamber is arranged in a plunger which is supported for axial movement within said housing configured as a cylinder. Finally, the sample chamber is provided in the form of a diameter reduction of the plunger.
Basing on the above-described prior art an object of the present invention is to improve a sampling apparatus of this type to the effect that representative samples of product can be retracted from a product chamber in a simple and inexpensive manner, with an adequate sealing being provided between the product outlet and said product chamber and the danger of pollution of the sample chamber being as little as possible.
The solution of this problem provides that during normal operation the sample chamber is in its position projected into the product chamber and is movable toward the product outlet area only for the purpose of retracting the sample of product, and that the piston is sealed against the housing between the product outlet and the end of the housing protruding into the product chamber, by means of a sealing ring and preferably an O-ring.
Accordingly, the sampling apparatus of the invention is improved over prior art to the extent that during normal operation the sample chamber within the product chamber is constantly traversed by a flow of the product to be extracted, in particular by a liquid, whereby it is guaranteed that a representative sample is retracted at any time during the sampling. It is prevented, for example, that a sample of product is retracted which for reasons of time has already experienced alterations due to storage thereof in the sample chamber for an extended period of time already. Since there is a constant flow of the product to be retracted through the sample chamber, no material will adhere to it. Also, any medium remaining in the sample chamber after sampling is unable to bond, bake and/or adhere to sample chamber within the time in which the sample chamber is not inserted in the product chamber, since this period is set extremely short by the fact that the sample chamber is retracted from the product chamber only for the purpose of sampling and is returned to the product chamber as soon as the sample of product has been collected. Important in this context is the sealing ring which allows to obtain a sealing of the product chamber against the product outlet, so that the product can neither escape via the product outlet nor gaseous or liquid surrounding media enter into the product chamber.
According to another feature of the invention it is provided that the sealing ring is inserted in a recess in the inner lateral side of the housing. This configuration guarantees that the sealing ring is always present where it is needed and provides for a sufficient sealing effect between the plunger and the housing.
According to still another feature of the invention it is provided that the housing has a recess in the region of the sample chamber in its projected position. This recess serves for receiving the product during sampling. In this context it turned out to be advantageous if the said recess is formed as bore, of which the diameter is slightly smaller than the length of the sample chamber, so that the sample chamber can be rapidly and completely charged via said recess.
In particular, said bore is formed as a continuous bore so as to have access openings on both sides of the sample chamber allowing in case that the sample chamber is traversed by the product flow.
An advantageous further development of the apparatus according to the invention provides that the piston on the free end thereof in the region of the sample chamber has a sealing ring that is preferably configured as an O-ring. With this configuration the apparatus is also suited for very mobile media like solvents, for example, when the same are under high pressure. The additional sealing ring additionally seals the product outlet against the product chamber, so that even during sampling with the sample chamber arranged in the area of the product outlet any additional product can neither penetrate from the product chamber nor foreign matter enter the product chamber. This is particularly important when a fixed amount of sample of product is to be retracted at every sampling action.
Preferably, said sealing ring is inserted in a recess in the plunger, so that it provides for smooth sealing against the housing in any position of the plunger.
According to another feature of the invention a cup holder for receiving non returnable cups is detachably mounted to the product outlet. These non returnable cups offer the possibility of retracting samples of product rapidly and easily, a fresh cup being used for every sampling action in order to avoid the collected sample of product from being impaired and above all from being polluted.
Finally, an improvement of the apparatus according to the invention provides for the product outlet and cup holder to be connectable to each other via a bayonet catch in order to simplify and shorten the working steps necessary for sampling and for the subsequent preparation of the apparatus for new sampling.